Shape memory alloy heat pump

Abstract

The present invention relates to a shape-memory alloy (SMA) heat pump system comprising at least three shape-memory alloy (SMA) cores, a loading / unloading mechanism for converting the SMA cores from one crystalline state to another, allowing each core to dissipate heat when loaded and absorb heat when unloaded, a fluid supply system comprising one or more fluid lines of a specific volume for supplying fluid to the SMA cores, a set of controllable orifices positioned between each SMA core, allowing multiple fluid supply paths to supply fluid, and a controller implementing specific control parameters and logic for controlling the loading and unloading of the SMA cores, the flow rate of fluid through the fluid supply system, and the opening and closing of the orifices, so that an optimal cycle is achieved to maximize heat recovery.

Description

[Technical Field]

[0001] This disclosure relates to shape memory alloy (SMA) heat pumps, and more particularly to heat recovery in the heat pump cycle to improve efficiency in solid-state SMA heat pumps. [Background technology]

[0002] Recent research into the elastocaloric (EC) effect has demonstrated its potential as a solid-state alternative to traditional vapor compression cooling, refrigeration, heat pumps, etc. EC cycles utilize the superelastic behavior of shape memory alloys (SMAs), thereby facilitating heat absorption from a cold source and heat release to a hot sink through cyclic uniaxial loading and unloading.

[0003] Recently, there has been considerable interest in using SMA materials in the manufacture of energy recovery devices and heat pump / refrigeration systems. One example of the use of SMA plates is a heat pump device comprising at least one stack of plates, where at least two plates are formed and assembled from SMA material, and the SMA plates have one or more fluid ports adapted to allow a working fluid to pass through the stack. An example application of such an SMA stack is disclosed in PCT Patent Publication No. WO 2021 / 219667 (Patent Document 1), assigned to Exergyn Ltd.

[0004] Heat pump (HP) technology has gained wide commercial acceptance in heating, ventilation, air conditioning, and refrigeration (HVAC-R) applications. HP technology can offer energy savings and reduced emissions, and is typically installed in heating and cooling systems in buildings and automobiles.

[0005] Heat pumps using SMA tubes are known in the art. SMA refers to an alloy that retains its shape when deformed by an external force below a critical temperature, but when heated to the critical temperature, the shape memory effect is activated and the alloy returns to its original shape due to a shape recovery force. SMAs, such as titanium-nickel alloys, are formed into a predetermined shape at high temperatures.

[0006] One example of an SMA heating and cooling system is described in U.S. Patent No. 10,823,465 to Radermacher et al., which discloses a heating and cooling system using multiple elastocaloric or thermoelastic modules arranged in pairs. Thermal waves are used to describe how fluids of different temperatures move through the system, controlled by appropriately positioned pumps. Thermal waves are a term used to describe fluids moving through the system to define the thermal profile of the fluid at different times during operation. A problem with this system is that the fluids are difficult to mix, resulting in inefficient operation. This also results in inefficient heat recovery in the thermoelastic modules between cycles.

[0007] Due to the cyclical nature of the state changes in SMA-based heat pump systems, it is desirable to make the system as energy-efficient as possible. In embodiments of heat pump systems, one or more SMA cores can be interconnected. Figure 1 shows a prior art heat pump system in which hot and cold fluid streams are flown through an SMA core, and the core is driven by a mechanical force between cycles. For example, during operation, the internal fluid temperatures of the heat exchanger may be 35.25°C on the hot side and 6.8°C on the cold side. Therefore, for the heat pump to operate, the temperature of the SMA must be above 35.25°C to release heat to the hot stream and below 6.8°C to absorb heat from the cold stream. In this example, the temperature of the SMA must change by approximately 30°C between the heat absorption and heat release phases of operation. Due to the thermal mass of the SMA, a significant amount of energy is required to achieve this temperature change. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2021 / 219667 [Patent Document 2] U.S. Patent No. 10,823,465 Summary of the Invention [Problem to be solved by the invention]

[0009] There is therefore a need for an SMA heat pump that maximizes heat recovery from the heat available between heat release and heat absorption, and this forms the object of the present invention. [Means for solving the problem]

[0010] The present invention relates to a heat pump system and a heat pump control method as set forth in the accompanying claims.

[0011] In one embodiment of the present invention, at least three shape-memory alloy (SMA) cores; a loading / unloading mechanism that converts the SMA cores from one crystalline state to another, allowing each core to dissipate heat when loaded and absorb heat when unloaded; a fluid supply system comprising one or more fluid lines of a specific volume for supplying fluid to the SMA core; a set of controllable orifices disposed between each SMA core, the set of orifices allowing multiple fluid supply paths to supply fluid; a controller that implements specific control parameters and logic to control the loading and unloading of the SMA core, the flow rate of fluid through the fluid supply system, and the opening and closing of orifices during operation to ensure that an optimal cycle is achieved to maximize heat recovery; A heat pump system comprising:

[0012] In one embodiment, a fluid pump is placed in one of the fluid lines leading to or coming from the heat sink and / or heat source, and the pump is located in a part of the circuit where the fluid is at a nearly constant temperature. By placing the pump away from the part of the circuit where there is a temperature gradient, it does not disrupt the thermal waves circulating through the system for heat recovery. The thermal mass of the pump does not interfere with heat recovery.

[0013] In one embodiment, at least three shape memory alloy (SMA) cores operate out of phase with one another, and the operation of the SMA cores is set out of phase using the formula N / 360 degrees, where N is the number of SMA cores in the system.

[0014] In one embodiment, a set of controllable orifices is located at points between each SMA core, allowing three different fluid flow paths.

[0015] In one embodiment, the three different fluid flow paths are: a flow path from the previous SMA core to the heat source and from the heat source to the next SMA core; a flow path from the previous SMA core to the heat sink and from the heat sink to the next SMA core; A flow path from the previous SMA core directly to the next SMA core.

[0016] In one embodiment, the fluid flow path comprises a pipe, and when connected from one SMA core to the next, the shape and volume of the length of pipe between them is tailored to a specific value to optimize heat recovery using thermal waves in the fluid.

[0017] In one embodiment, a variable speed fluid pump variably controls the fluid flow rate, allowing for optimal operation at different cycle times.

[0018] In one embodiment, a check valve is placed in the fluid line between the two SMA cores after the controllable orifice to prevent fluid from flowing in the wrong direction while the orifice is opening or closing, minimizing mixing.

[0019] In one embodiment, the heat pump system of any of the preceding items, wherein the fluid supply system includes a valve assembly disposed between two SMA cores, the valve assembly configured with at least three SMA cores to perform the following steps: a. Supplying heated fluid from a previous SMA core to a heat source and from the heat source to a next SMA core. b. Dispensing cooled fluid from the previous SMA core to a heat sink and dispensing fluid from the heat sink to the next SMA core. c. Providing fluid from a previous SMA core to a next SMA core.

[0020] In one embodiment, the fluid volume between one SMA core and the next can be switched between two different volumes, one volume optimized to operate at peak power and the other volume optimized to operate at peak Coefficient of Performance (COP).

[0021] In one embodiment, the fluid volume between one SMA core and the next is variable between a minimum and a maximum, and the fluid volume can be optimized for any operating point between and including the peak power and peak COP operating points.

[0022] In another embodiment at least three shape-memory alloy (SMA) cores; a loading / unloading mechanism that converts the SMA cores from one crystalline state to another, allowing each core to dissipate heat when loaded and absorb heat when unloaded; a fluid supply system comprising one or more fluid lines of a specific volume for supplying fluid to the SMA core; a set of controllable orifices disposed between each SMA core, the set of orifices allowing multiple fluid supply paths to supply fluid; a fluid pump positioned in one of the fluid lines leading to or coming from one or both of the heat sink and the heat source so as to be located in a fluid at a substantially constant temperature; A heat pump system comprising:

[0023] In yet another embodiment, a method of controlling a shape memory alloy heat pump system includes: disposing at least three shape-memory alloy (SMA) cores in communication with one another; Loading / unloading the SMA cores to convert them from one crystalline state to another such that each core dissipates heat when loaded and absorbs heat when unloaded; providing fluid to one or more fluid lines of a specific volume to supply the fluid to the SMA core; disposing a set of controllable orifices between each SMA core to allow multiple fluid supply paths to supply fluid; Controlling the loading and unloading of the SMA core, the flow rate of fluid through the fluid supply system, and the opening and closing of orifices during operation; A method is provided which includes: [Brief explanation of the drawings]

[0024] The invention will be more clearly understood from the following description of embodiments thereof, given by way of example only, with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 is a high-level system diagram of a heat pump system. [Figure 2] 1 is a graph showing how heat recovery is achieved by using the temperature gradient of the fluid exiting the core as the temperature gradient entering the core at a later time. [Figure 3a] 1 shows a heat pump system with a single SMA core according to a first embodiment of the present invention. [Figure 3b] 1 shows a heat pump system with two SMA cores according to a first embodiment of the present invention. [Figure 4a]1 shows a heat pump system with a single SMA core according to a second embodiment of the present invention. [Figure 4b] 1 shows a heat pump system with two SMA cores according to a second embodiment of the present invention. [Figure 5a] 1 shows a heat pump system with three SMA cores according to a third embodiment of the present invention. [Figure 5b] 1 shows a heat pump system with four SMA cores according to a third embodiment of the present invention. [Figure 5c] 1 shows a heat pump system with five SMA cores according to a third embodiment of the present invention. [Figure 5d] 1 shows a heat pump system with four SMA cores divided into two stacks per core and run as a two-stage cascade according to a third embodiment of the invention. [Figure 6] We show that the performance of the heat pump can be changed by changing the volume of fluid in the piping between the cores of the heat pump system shown in Figure 5. [Figure 7] We show that the performance of the heat pump can be changed by changing the volume of fluid in the piping between the cores of the heat pump system shown in Figure 5. [Figure 8a] 1 shows a heat pump system with four SMA cores according to a fourth embodiment of the present invention. [Figure 8b] 5 shows some embodiments of a heat pump system according to a fourth aspect of the present invention. [Figure 8c] 5 shows some embodiments of a heat pump system according to a fourth aspect of the present invention. [Figure 8d] 5 shows some embodiments of a heat pump system according to a fourth aspect of the present invention. [Figure 8e] 5 shows some embodiments of a heat pump system according to a fourth aspect of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] The operation of heat pumps using SMA materials is known and described in detail in commonly assigned PCT Patent Publication No. WO2019 / 149783, the contents of which are incorporated herein by reference in their entirety. The present invention particularly relates to heat pump systems having one or more SMA cores within the system. The or each core may be a single SMA core, with one or more plates of SMA material arranged in a stacked configuration. The SMA core may also be constructed from sheets and / or ribbons of SMA material, or any shape. Any calorific material may be used to implement the heat pump system of the present invention.

[0026] FIG. 1 is a high-level system diagram of an SMA material-based heat pump system, generally designated by the reference numeral 10. Housing 11 contains one or more SMA cores in fluid communication with heat sinks and heat sources 12, 13. The heat pump is configured to pump heat from a heat source (usually cooler) to a heat sink (usually hotter). In air conditioning / refrigeration, the reverse is used. One or more fluid streams, both hot and cold, are flowed through the SMA core, subjecting it to variable stresses. For example, during operation, the internal fluid temperatures may be 36°C at heat sink 12 and 6°C at heat source 13. Therefore, for heat pump 10 to operate, the temperature of the SMA material must be above 36°C to reject heat to the hot stream and below 6°C to absorb heat from the cold stream.

[0027] Either heat stored in the SMA core when it was previously hot, or heat from a second core that is now hot, can be used to bring the temperature of the cold core close to the temperature required for heat dissipation. In the simplistic case, if the cold and hot cores are thermally connected, they will reach equilibrium at an intermediate temperature, reducing heat loss by half. However, by replicating the behavior of a counterflow heat exchanger, it is possible (assuming infinite time and thermal conductivity) to fully heat the cold core to the required temperature and simultaneously fully cool the hot core to the required temperature.

[0028] Figure 2 is a graph showing how heat recovery is achieved by using the temperature gradient of the fluid exiting the core as the temperature gradient entering the core at a later time. This is shown as *1 in Figure 2. Figure 2 shows the ideal temperature profile of the fluid entering and exiting the core, along with the actual core temperature. The phase shift between the exiting and entering fluids occurs over the length of the core. If the temperature of the fluid exiting the core is higher than the "hot in" 16 temperature, it is directed to the "hot out" 17 flow into the heat sink 12. Similarly, if the temperature of the fluid exiting the core is lower than the "cold in" 14 temperature, it is directed to the "cold out" 15 flow into the heat source 13. If the exiting fluid is between these two temperatures, a heat recovery system is required to preserve this temperature gradient and use it as the fluid entering the core later in the cycle, or in a different core. (*1) For optimal performance, the temperature difference between the entering fluid and the material should be minimized. (*2) Furthermore, the temperature difference between the material and the outgoing fluid should be minimized on both the hot and cold sides(*3).

[0029] According to a first aspect of the present invention, there is provided a heat recovery system for realizing point *1 in Figure 2. The present invention achieves this by storing the temperature gradient of the fluid emerging from the SMA core for later use.

[0030] FIG. 3a shows a heat pump system with a single SMA core, designated by reference numeral 30. Fluid can enter one side of the core 30 at the inlet and exit at the outlet. As the fluid exits the core, it is split into multiple streams by a valve assembly 31. Each stream has a different, relatively constant temperature. Another valve assembly 32 is disposed in fluid communication with the inlet of the core 30. The fluid in the streams is then sequentially admitted to the core for heat recovery, as controlled by the valve assemblies 31 and 32. The more streams there are, the better the heat recovery performance.

[0031] As shown in Figure 3a, the SMA core 30 requires a pump 37 and two sets of 1:ns-way valves (where "ns" is the number of heat recovery streams plus the number of heat sink and heat source streams) to direct the fluids, shown as valve assemblies 31 and 32. Six heat recovery streams are shown, thus requiring 1:8-way valves at the inlet and outlet of the SMA core 30. Any number of heat recovery streams can be used. Timing is completely flexible, allowing for high performance. Each stream requires a fluid storage volume 33 (HR1 through HR6) because there are times when fluid can be pumped into a stream without being removed, and times when fluid can be removed without being supplied. The heat sink and heat source lines also require fluid storage volumes 34 and 35. The pump 37 must have low thermal mass and low thermal conductivity to prevent the different fluid streams from mixing. It will be understood that with a single core, each stream can only be in one of three states: idle, filling, or draining, since fluid is never drawn from the same line that it draws fluid from.

[0032] Figure 3b shows a heat pump system with two SMA cores (this time with two cores) according to the first embodiment of the present invention. The second core also requires its own fluid pump and inlet and outlet valve sets. The heat recovery streams (HR1 through HR6), heat sinks, and heat sources are shared with the first core. Preferably, but not necessarily, core 2 can be operated 180° out of phase with core 1, which reduces fluid storage volume and keeps flow rates through any part of the circuit more consistent. Any number of cores can be added in this manner, each requiring its own set of valves and pumps. Ideally, each core is operated 360 / n cores out of phase, where n cores is the number of cores in the system.

[0033] FIG. 4a shows a heat pump system with a single SMA core, designated 40, that utilizes a temperature gradient flow of fluid to heat or cool the core. Fluid can enter one side of the core 40 at the inlet and exit at the outlet. As the fluid exits the core 40, it is split into multiple streams by a valve assembly 41. In this example, there are four streams: heat sink, heat source, HR1, and HR2. Another valve assembly 42 is placed in fluid communication with the inlet of the core 40. The fluid exiting the core 40 is stored under a temperature gradient across two heat recovery volumes 43 and 44. These fluid volumes are used for heat recovery later in the cycle. The better the temperature gradient can be maintained within the heat recovery volumes, the better the performance.

[0034] The set of valves 42, 41 is only a 1:4-way valve, reducing complexity compared to Figure 3a. Timing remains fully flexible, improving performance. Each heat recovery stream requires a fluid storage volume 43, 44 to allow the stream to be "filled" and "drained" for each cycle. Pump 45 is required for circuits with temperature gradients. Therefore, pump 45 should have low thermal mass, low thermal conductivity, and should not mix fluids.

[0035] Because fluid storage volumes are required within the heat recovery volumes 43 and 44, it is desirable to have a pipe with fluid entering and exiting the volume at one end and a fluid reservoir at the other. This maintains a constant temperature in the fluid reservoir and limits mixing. Thus, if a fluid stream is stored with a temperature gradient rising from 10°C to 30°C, its withdrawal later in the cycle will result in a reversal: initially, 30°C fluid leaves the reservoir, and then drops back down to 10°C when the reservoir is fully withdrawn. This "reversal" of the fluid temperature gradient means that the stored fluid is used to warm the core when it is cooling. Therefore, a second storage volume is included to store fluid when the core is heating and then used to cool the core.

[0036] It will be understood that this system can operate using multiple cores, with each core having its own dedicated pair of heat recovery streams, pair of valve assemblies, and pump. Figure 4b shows a heat pump system with two SMA cores, each with its own dedicated pump, valve assembly, and heat recovery volume. The two cores share the same heat sink and heat source. As the number of cores increases, ideally, each core can be operated 360 / n cores out of phase, where n cores is the number of cores in the system.

[0037] Adding more cores to the system improves overall system performance by providing a more consistent flow through the heat source and heat sink. It has been found that with three or more cores, 100% utilization of the heat sink / heat source is achieved. Ideally, a heat pump system would have three cores, each with its own dedicated heat recovery system, as shown in Figures 4a and 4b.

[0038] Figures 5a, 5b, and 5c show three embodiments of a heat pump in a third embodiment utilizing three, four, and five cores, respectively. The heat pump utilizes a thermal wave heat recovery concept and can operate with more than two cores. Different numbers of cores will change the relative times for heat release / absorption and heat recovery. Table 1 below shows some examples of the times for heat release / absorption and heat recovery for a given number of cores, where each cycle consists of 360°.

[0039] Applications requiring a large delta-T (temperature difference) may benefit from using more cores since more time will be spent recovering heat. Applications with a small delta-T may benefit from selecting fewer cores since less time will be spent recovering heat.

[0040] During operation, exactly one core dissipates and absorbs heat, while the remaining cores recover heat. With five or more cores, it is possible for exactly two cores to dissipate and absorb heat, while the remaining cores recover heat.

[0041] [Table 1]

[0042] Figure 5a shows a heat pump system utilizing thermal wave heat recovery, with three SMA cores, designated by reference numerals 50, 51, and 52. Between each core is a set of controllable orifices VB1 53, VB2 54, and VB3 55, which direct the fluid in one of three directions: 1.Transportation to and from the heat source 2.Communication with the heat sink 3. From one core to the next

[0043] The VB can be located anywhere along the pipe from one core to the next. However, it is advantageous for performance to locate the VB near the fluid source core, with the majority of its length in the pipe leading to the next core. In the diagram, the VB is depicted in the center of the two cores. Also, while all five controllable orifices are depicted as a group, the controllable orifices between the heat sink and heat source can be located anywhere along the line. A controller is provided to control the set of controllable orifices VB1 53, VB2 54, and VB3 55. The controller is programmed with specific parameters and logic software to control the loading and unloading of the SMA cores, the flow rate of fluid through the fluid delivery system, and the opening and closing of the orifices during operation to achieve an optimal cycle for maximizing heat recovery.

[0044] An optional check valve can be installed after each controllable orifice connecting two cores. This prevents fluid from flowing backward through the circuit during the short time it takes for the valve to open or close. For very fast acting valves, the check valve can be omitted.

[0045] The volume and shape of the pipe connecting the two cores is important to achieve an optimal cycle and maximize heat recovery. The pipe must be sized so that the thermal wave can propagate along the length of the pipe and to the next core within the available time. This can be adjusted for a given pipe volume by adjusting the flow rate and cycle time. Adjustments to flow rate and cycle time can be controlled by a controller. For example, if the flow rate is doubled, the cycle time must be halved for a given fixed pipe volume.

[0046] While pump 56 is shown in Figure 5a as being located in the line to the heat sink, it could also be located in the line from the heat sink, or in the line to or from the heat source. Additionally, a second pump can be placed at the heat source to lower the head the pump experiences. Doing so in a three-core system would cause the pump's head to vary throughout the cycle, but this is not an issue in a four-core system. This improves performance over competing designs because the pump is not located in a temperature gradient within the fluid. If the pump were located in a temperature gradient, its thermal mass would mix with the fluid, disrupting the gradient. By placing the pump in the heat sink / heat source pipeline, mixing of the thermal mass with the fluid is not an issue.

[0047] Figures 5b and 5c show four-core and five-core embodiments of the same concept. The layout is the same, with additional cores 61, 63 and VBs 62, 64 connected. The only change is the control software, which controls the valves at different times depending on the number of cores in the system, to maintain the timings shown in Table 1. The four-core embodiment has the potential advantage of being able to include an optional second pump 60 on the heat source line without the problem of head varying throughout the cycle.

[0048] It will be appreciated that the embodiments shown in Figures 5a, 5b, and 5c have several advantages over the other circuits presented. Only five valves per core are required for efficient heat recovery operation. Compared to the embodiments of Figures 3 and 4, no fluid volume storage is required because all pipes always flow at the same speed. 100% utilization of the heat source / heat sink minimizes temperature differences between each core. Furthermore, the pump can be installed on a constant temperature line, allowing for high thermal mass / thermal conductivity without fluid mixing issues.

[0049] In other embodiments, the fluid volume between the cores can be varied to provide a two-volume fluid system to improve or extend the performance envelope of a solid-state heat pump using heat recovery. In Figures 5a, 5b, and 5c, the length of the pipe connecting the cores is fixed to provide a fixed volume of fluid between the cores.

[0050] Figure 5d shows an embodiment of the third concept, utilizing four cores but operating as a two-stage cascade. Such a system is necessary to achieve a higher delta-T than is possible with a single stage. Such systems typically use different SMA materials for stacks 1 and 2, each tuned for a different temperature range. Figure 5d shows a similar arrangement to Figure 5b, except that two valve systems for each of VB1, VB2, VB3, and VB4 are interconnected. The purpose of this connection is to use the heated fluid exiting the cold stage as the cold inlet for the hot stage. In the reverse direction, the cooled outlet from the hot stage is used as the hot inlet for the cold stage. Connecting two systems in this manner increases the delta-T in a two-stage cascade while maintaining all the heat recovery benefits of Figures 5a, 5b, and 5c. In this example, two valves from each set are redundant and can be removed, resulting in a total valve count less than twice that required for a single stage. The method used to connect two systems to form a cascade can be applied to any of the concepts shown. Simply connect the "hot out" of the cold stage to the "cold in" of the hot stage, and the "hot out" of the cold stage to the "cold in" of the hot stage.

[0051] In the systems shown in Figures 5a through 5d, the fluid volume between the cores is fixed, allowing the performance of the device to be varied by adjusting the cycle time. Because the fluid volume is fixed, the flow rate is adjusted inversely proportional to the cycle time, maintaining optimal phase of the thermal waves throughout the circuit. However, a fixed fluid volume is only optimal for a certain cycle time. Increasing the cycle time requires a lower than optimal flow rate. Decreasing the cycle time requires a higher than optimal flow rate. A solution to this problem is to create a system where the fluid volume between the cores can be adjusted depending on the current operating point.

[0052] Figures 6 and 7 show modeling results that show higher CoPs for different volumes depending on the heat output. The graphs in Figures 6 and 7 show CoP vs. kWth for heating and Energy Efficiency Ratio (EER) vs. kWth for cooling, for a four-SMA-core heat pump embodiment. In an ideal system, continuously varying the volume would always result in a peak COP / EER for the required heating / cooling output. However, most of the performance improvement can be achieved by using only two separate volumes. In the example in Figure 6, when operating at heating outputs below 5 kWth (dark vertical line), a 3 L fluid volume would be used. When operating at higher heat outputs, a 2 L volume would be used. A system without the flexibility to vary the fluid volume would need to choose an intermediate volume, such as 2.5 L, which would result in a lower COP at most operating points.

[0053] For cooling, as shown in Figure 7, a fluid volume of 3 liters is best below 3.7 kWth, and a volume of 2 liters is optimal above 3.7 kWth.

[0054] With a simple three-way valve and additional piping on each line between the cores, two separate volumes can be created: when the valve is in one position, the fluid path is 2L, and when the valve is in the other position, additional piping is connected, making the fluid volume 3L.

[0055] By providing a telescopic pipe section in each pipeline between the cores, a continuously variable pipe section can be created. Extending the telescopic piece increases the volume. Retracting the telescopic piping reduces the volume again.

[0056] FIG. 8a shows a heat pump system according to a fourth aspect of the present invention, including four SMA cores 80a, 80b, 80c, and 80d. In this embodiment, fluid passes through the SMA cores in different directions at different times during the cycle. Alternating fluid flow direction can increase the efficiency of the SMAs. The advantage is that one end of the core is always hotter than the other, so no single SMA experiences the entire temperature range of the heat pump. This narrower temperature range of the SMAs improves their performance. While the illustrated configuration is a four-core embodiment, the present invention can be used with any number of cores. The advantage of using four cores is that the heat exchangers are fully utilized, reducing the overall temperature difference and resulting in consistent pumping performance. In the present invention, pumps 81 and 82 are located on or near a heat source 83 and a heat sink 84. Pumps 81 and 82 operate continuously at a constant speed. Fluid from the heat source 83 is pumped through each of the four cores in the order 1, 3, 2, and 4, with the heat release and absorption portions of the cycle separated by 180°. The remaining portion of the cycle is spent in heat recovery. During heat recovery, pistons 85 and 86 are used to simultaneously pump fluid into and out of the two cores. The pistons can be replaced with bidirectional pumps. Fluid volumes HR1a through HR4b store fluid with a temperature gradient spanning HR1a through HR4b. During heat recovery, this temperature gradient flows through the cores and is used to change the core temperature from hot to cold, or vice versa. Fluid leaving the core during this phase is stored in the opposite HR volume for use half a cycle later. When the heat pump first starts up, these HR volumes will be at ambient temperature. It takes multiple cycles for a steady-state temperature gradient to form. The advantage of this embodiment is that a more consistent delta-T is achieved throughout the cores, which provides operational benefits, such as a longer lifespan for the SMA material.

[0057] The complete regulated cycle will be described, starting with the cooling phase. During the cooling phase of the cycle, fluid from the heat source 83 is pumped into the core while the core is unloaded. The core serves to cool the fluid. The fluid exiting the core is returned to the heat source while it is still cooler than the inlet temperature. In this way, cooling is provided to the heat source 83. Once the cooling is exhausted and the temperature of the fluid exiting the core matches the inlet temperature, a valve switches and the fluid is sent into the HRa circuit. Simultaneously, fluid from the HRb circuit enters the core. The incoming fluid is initially cold, but then slowly warms up to the inlet temperature. The idea is that the core is warmed by this fluid from the cold side temperature to the hot side temperature. At the same time, the fluid entering HRa is initially cold, but warms as the core warms, creating a temperature gradient within the HRa flow that will be used later.

[0058] Once the heat recovery process is complete, the fluid from the heat sink is directed into the core. At this point, the flow direction changes, and the hot fluid enters the core where it previously left. At this point, the core is under load, so it releases heat, heating the fluid within the core. The heated fluid then exits the core and enters the heat sink, warming it. Once all the heat has been removed and the core's outlet temperature matches the inlet temperature, the valve switches again, allowing fluid to flow from HRa into the core and back into HRb. Note that the flow direction has not changed again, so the HR is now flowing in the opposite direction from the previous half cycle. The fluid coming from HRa is initially warm, then slowly cools down to the cooler inlet temperature. This cools the core towards a lower temperature. The fluid leaving the core, which was initially quite hot, is directed into HRb, where over time the fluid temperature also decreases, creating a temperature gradient in HRb that is used by the HR for the next half cycle. Once the HR process is complete, the cycle begins again.

[0059] Figure 8b shows an embodiment of a single core 80 according to the fourth aspect of the invention. The heat sink 84 and heat source 83 include two optional control valves 90, 91. These allow the pumps 81, 82 to circulate fluid even when the core 80 is not connected. Alternatively, the control valves 90, 91 can be removed and the pumps 81, 82 can be operated intermittently. The heat recovery part of the circuit requires a single piston 85 or bidirectional pump.

[0060] Figure 8c shows a two-core embodiment 80a, 80b according to the fourth aspect of the invention. As with the single-core embodiment of Figure 8b, control valves are included in the heat sink and heat source to allow continuous operation of the pumps 81, 82. A piston 85 on the heat recovery circuit or bidirectional pump is shared between the two cores 80a, 80b. The two cores operate 180° out of phase with each other.

[0061] Figure 8d shows a four-core embodiment according to the fourth aspect of the invention. The arrangement is the same as Figure 8a, except that the valves in the heat recovery circuit have been removed. This is an optional simplification of Figure 8a, resulting in a simpler system with fewer parts. This is possible because the flow rate in these lines is controlled by the movement of pistons or bidirectional pumps. Therefore, unless these are operating, fluid cannot enter or leave the heat recovery circuit, making the valves in Figure 8a redundant.

[0062] Figure 8e shows a four-core, two-stage embodiment of the fourth aspect of the present invention. Such a system is necessary to achieve a higher delta-T than is possible with a single stage. Such systems typically use different SMA materials for stacks 1 and 2, each tuned for a different temperature range. Figure 8e shows a similar arrangement to Figure 8d, except that two systems are interconnected. The two systems are connected at the location where a single-stage system would have a heat sink / heat source. A pump is required between the two systems to maintain fluid flow between them. The purpose of the connection is to use the heated fluid exiting the cold stage as the cold inlet for the hot stage. In the reverse direction, the cooled outlet from the hot stage is used as the hot inlet for the cold stage. Connecting the two systems in this way allows for increased delta-T in a two-stage cascade while retaining all of the heat recovery benefits of Figures 8a and 8d.

[0063] It will be appreciated that the integrated core manifold and valve block can be mounted as close as possible to the core outlet for best performance, as the presence of fluid between the core and valve block will adversely affect performance when the flow direction changes.

[0064] As used herein, the terms "comprise, comprise, comprised, and comprising" or any variation thereof, and the terms "include, includes, included, and including" or any variation thereof, are considered to be fully interchangeable and all of them should be given the broadest possible interpretation, and vice versa.

[0065] The invention is not limited to the embodiments described hereinabove, which may be varied in both structure and detail.

Claims

1. at least three shape-memory alloy (SMA) cores; a loading / unloading mechanism for converting the SMA cores from one crystalline state to another, allowing each core to dissipate heat when loaded and absorb heat when unloaded; a fluid supply system comprising one or more fluid lines of a specific volume for supplying fluid to the SMA core; a set of controllable orifices disposed between each SMA core, the set of orifices allowing multiple fluid supply paths to supply fluid; a controller having specific control parameters implemented therein for controlling the loading and unloading of the SMA core, the flow rate of fluid through the fluid supply system, and the opening and closing of the orifice during operation; A shape memory alloy heat pump system comprising:

2. 10. The heat pump system of claim 1, further comprising a fluid pump disposed in one of the fluid lines leading to or from one or both of the heat sink and the heat source, the pump being located in a fluid at a substantially constant temperature.

3. 10. A heat pump system according to any one of the preceding claims, wherein the at least three SMA cores operate out of phase with each other.

4. 4. The heat pump system of claim 3, wherein the operation of the SMA cores is set to be out of phase using the formula N / 360 degrees, where N is the number of SMA cores in the system.

5. 10. A heat pump system according to any one of the preceding claims, wherein the set of controllable orifices is located at points between each SMA core, allowing three different fluid flow paths.

6. The three different fluid flow paths are a flow path from the previous SMA core to the heat source and from the heat source to the next SMA core; a flow path from the previous SMA core to the heat sink and from the heat sink to the next SMA core; a flow path from the previous SMA core directly to the next SMA core; The heat pump system according to claim 5 .

7. 10. A heat pump system according to any one of the preceding claims, wherein the fluid flow path comprises pipes, and when an SMA core is connected to the next SMA core, the volume of the entire length of pipe between them is a specific, adjusted value, so as to optimize heat recovery using thermal waves in the fluid.

8. 10. A heat pump system according to any preceding claim, wherein a variable speed fluid pump variably controls the flow rate of the fluid, allowing optimal operation at different cycle times.

9. 10. The heat pump system of claim 1, wherein a check valve is positioned in the fluid line between two SMA cores and after the controllable orifice to prevent fluid from flowing in the wrong direction while the orifice is opening or closing, thereby minimizing mixing.

10. The fluid supply system includes a valve assembly disposed between two SMA cores, the valve assembly, together with the at least three SMA cores, supplying heated fluid from a previous SMA core to a heat source and from the heat source to a next SMA core; supplying cooled fluid from a previous SMA core to a heat sink and from the heat sink to a next SMA core; providing fluid from a previous SMA core to a next SMA core; 10. The heat pump system of claim 1, configured to:

11. 10. A heat pump system according to any one of the preceding claims, wherein the fluid volume between one SMA core and the next can be switched between two different volumes, one volume optimized to operate at peak power and the other volume optimized to operate at peak Coefficient of Performance (COP).

12. 10. A heat pump system as described in any one of the preceding claims, wherein the fluid volume between one SMA core and the next SMA core is variable between a minimum and a maximum, and the fluid volume can be optimized for any operating point between and including a peak power operating point and a peak COP operating point.

Images